initially the tachometer worked intermittantly and when it stopped i used to press the air conditioning buttons and it used to start working.
now it is completely dead.
there is no amplifier under the hood.....only the pick up at the bell housing and the tachometer.
is the problem with the tach or the pick up

Look on the driver's side wheel well for a cylinder, about 1.5 inches in diameter and 2 inches high. Unscrew the top part from the car. You'll have a bell shaped part with a plug in it. Take the plug out of the bell shaped part (this can be hard...). Put a piece of foam or even a cigarette butt in the bell housing and put the plug back in. Screw it back on to the socket on the wheel well and try it.

Worked on mine and many others...

Nicolas

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1982 300D - http://members.xoom.com/nicodore/

You're right...that model does not have a "tach amp". That system is routed through the
EGR cotrol box in the right side of the passenger footwell. It is also tied into the A/C compressor control relay circuit(if it has a "D-Klima" relay). Since fiddling with the A/C controls used to make it work...I'd look there first. Its rare to have a tachometer or the sensor fail. You can test the sensor with a Voltmeter.
Randy

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W.R.Durrance
ASE Master Tech
Mercedes Tech 19 Years

I had the same symptoms on my '83 300D. Turns out I also did not have any back-up lights. This led me to believe that perhaps a fuse was blown. It was not. But, upon closer inspection I could see what appeared to be an oily film on most fuses. So I got out my can of electrical cleaner, and Presto! All is well in tach-land. I hope this helps!

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'83 300D-T